1. Field of the Invention
The present invention relates to a lens-fitted photo film unit having parts, which are made of transparent plastic and are exposed to the outside.
2. Description of the Related Art
An outer surface of a lens-fitted photo film unit has exposed optical parts of a taking lens, a viewfinder lens, a flash window and so forth, which are made of transparent plastic by means of injection molding. As to the lens-fitted photo film unit of a waterproof type, a unit body thereof is covered with a waterproof case, which is also made of transparent plastic by means of injection molding. The unit body contains not only a photographic film loaded in advance but also a built-in photographing mechanism including a shutter device.
The transparent parts are sometimes touched by a finger when the lens-fitted photo film unit is used and carried. In particular, when the waterproof type is used at the beach, cosmetics of suntan lotion and so forth sometimes adhere to the waterproof case. Some of such cosmetics make the transparent plastic clouded due to a chemical change so that transparency of the plastic is deteriorated, such as described in Japanese Patent Laid-Open Publication No. 7-104367. This harmful effect is improved by using AS (acrylonitrile styrene) resin as the transparent plastic, which is the material of the waterproof case.
The AS resin is superior regarding heat resistance, weather proof, resistance to chemicals, and impact resistance. Moreover, the AS resin has high transparency. In light of this, the AS resin is preferable as the material of the waterproof case and the optical parts exposed to the outside. The AS resin, however, generates a gas damaging photographic properties when surrounding temperature becomes high. In this case, it is confirmed that the xe2x80x9cfogxe2x80x9d is caused on the photographic film. The lens-fitted photo film unit is soled in a state that this film unit is enclosed in a dampproof gusset envelope. In the case of the waterproof type, the lens-fitted photo film unit is further sealed up in the waterproof case. Due to this, the gas generated from the AS resin under a high-temperature condition is accumulated in the waterproof case and the gusset envelope so that the fog is caused on the photographic film loaded in the lens-fitted photo film unit in advance.
In view of the foregoing, it is a primary object of the present invention to provide a lens-fitted photo film unit having transparent plastic parts exposed to the outside, in which a material of the transparent plastic parts is improved so as to prevent the parts from becoming clouded when a certain sort of cosmetic adheres thereto.
It is a second object of the present invention to provide a lens-fitted photo film unit having transparent plastic parts exposed to the outside, in which it is prevented that fog is caused on a photographic film due to occurrence of a gas damaging photographic properties.
In order to achieve the above and other objects, the transparent plastic parts exposed to the outside of the lens-fitted photo film unit are formed by means of injection molding on condition that one of methacrylate styrene resin and methacrylate butadiene styrene resin is used. As to the transparent plastic parts, there are a taking lens, a viewfinder lens, a flash window and so forth. Besides these, there is an underwater case employed for the lens-fitted photo film unit of a waterproof type.
According to the present invention, a poisonous gas causing photographic-film fog is prevented from rising, and the transparent parts are hardly clouded even if cosmetics of suntan lotion or the like adhere thereto. Thus, it is possible to easily enjoy taking a picture at a beach, a pool side and so forth.